Primary among the objectives of this project is the elucidation of cellular mechanisms involved in chemoreception and cellular response, particularly regarding cell motility. Theories are constructed to relate macroscopic mobility coefficients to microscopic response parameters and experiments are performed with both bacterial (E. Coli) and mammalian cells (leukocytes). New assay systems, involving laser light scattering and time-lapse cinemicrography are employed, and procedures are devised to isolate materials from cell surfaces for assay on reconstituted lipid bilayers.